Back in the olden times Aircraft Cylinder & Turbine sponsored the Rare Bear and quite often after we'd blow up an engine, because we had no spare, once we got the engine off of the airplane and transported it back to their facility in N. Hollywood several crew members would shift from working on the airplane in the hangar to assisting on the engine at the engine shop, myself included.
AC&T had a test cell that was basically an 18-wheeler with a shortish trailer. Towards the front of that trailer there a little enclosed cab with all of the gages and controls that faced aft with window that looked at a structure that was built to accept engine mounts for most of the common radial engines that they worked on. So you'd mount an engine mount on the the back of the trailer. Hang an engine off the back of the trailer and head for an airport (KWHP was right down the street, but eventually they started complaining so that truck/stand ended up having to go to Mojave) to test it. Once you got to the airport you'd mount a test club. A test club is a wooden fixed pitch prop that was calibrated so accurate performance testing could be performed using charts, graphs and calibrated instruments while also moving enough air to keep the cylinder head and oil temps under control using some weird generic rattle-trap cowl/oil cooler contraption during prolonged break in runs.
We were never able to run our engines at full power on the test stand, they tried that once and the trailer started to lift the tires on one side almost off of the ground before they got things under control. So we'd do the preliminary testing on the stand, take it off, transport it to Van Nuys, mount it and that big three-blade prop on the airplane and start testing it again. We had no way to securely chain the airplane down to the ground at three points but we could connect the tail hook structure securely enough to at least keep it from moving forward under a decent amount of power.
Even that was not enough to put full smash on the engine because it would start lifting the right MLG tire off the ground at about 70% of what the engine could deliver. Some of my best memories of working on that thing took place at probably 1-2am with the thing chained down just making beautiful noises with the entire exhaust system glowing red hot and blue/white flames shooting out halfway down both sides of the fuselage. Then we'd tow it back to the hangar and look it over, if everything looked okay we'd all go home and let the thing cool off. Then we'd show up the next day, look it over again and if everything was okay we'd cowl it up, load it for bear and kick it out the door so we could finally put the full beans to it, nitrous and everything, in the air because that was the only place to get accurate numbers about how much power this engine was actually making.
The point is the airplane could've torque rolled from a dead stop on the ground. Think about the rotating mass of hardened steel and aluminum in that situation, for every action there's an equal and opposite reaction.
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